In the manufacture of mercury-wetted, sealed contact switches, an end portion of an elongate article referred to as a stem is plated with nickel to promote the wettability of such end by mercury after the stem is assembled into a glass envelope of the switch. However, at the same time, care must be taken to retain the center portion of the article free of such nickel plate. Such center portion is to be sealed into the glass wall of a switch, and the nickel plate is known to exhibit poor adhesion to glass. To treat or plate one end of such an article may be expensive unless simple mass handling procedures can be employed.
To plate a predetermined length of one end of the articles in an economically feasible manner in accordance with the prior art, the articles are typically loaded, according to one particular method, into a plating rack wherein they abut against a magnetic holding plate which then retains the abutting ends of the articles. The holding plate serves simultaneously as a reference plane for the longitudinal positioning of the articles and provides electrical contact to the articles, to couple each of such articles into the plating circuit.
One disadvantage of such a prior art holder is that the contact resistances between the articles and the holding plate of the rack are not uniform. The result is a variation in the plating thickness from one article to another. A most serious situation occurs, however, when some of the articles, even though they are apparently held against the holding plate, receive a completely insufficient plating deposit or no plating deposit at all. It appears that a thin corrosion film or corrosion particle, which is likely to be found near electrolytic treating facilities, may become interposed between some of the articles and the holding plate to effectively insulate the particular article from the plating circuit.
Another disadvantage of the prior art plating rack relates to the holding power of the magnetic field. When the free ends of the articles extend downward from the rack into the plating bath, some of the articles are released at times from the rack, whereupon the articles either drop into the plating bath, from where they have to be removed, or they attach themselves to adjacent articles as they fall through the induced magnetic field of such articles. Of course, these attached articles disturb the electric fields in the plating bath thereby causing irregular current densities which, in turn, affect the plating deposits on neighboring ones of the articles, as well as on those which become linked by the magnetic attachment.
It appears desirable to have a more efficient facility for supporting articles above a plating bath. It is further desirable to include in such a facility a simple and reliable contact to each of the articles, such that the electric field generated about each of the articles in the plating bath is for all practical purposes equal to the field located about all the other articles.